1. Field of the Invention
The present invention relates to a jig for use in firing of ferrite-made product. More particularly, the present invention relates to a jig which enables firing of ferrite-made product (e.g. deflection yoke) with high dimensional accuracy.
2. Description of Related Art
Ferrite-made electronic parts such as deflection yoke and the like have conventionally been subjected to a firing treatment by inserting a deflection yoke 1 (shown in FIG. 1(c)) to be fired, into the hole 3 of a jig 2 (shown in FIG. 1(b)), then ordinarily piling up a plurality of such jigs as shown in FIG. 1(a) and placing the piled material in a firing furnace, or by inserting deflection yokes 1 into a plurality of holes 3 of a jig 2 (shown in FIG. 2(a)) with each ring 4 placed between each yoke 1 and each hole 3, piling up a plurality of such jigs as shown in FIG. 2(b), and placing the piled material in a firing furnace. The jig 2 and ring 4 used above have generally been made of mullite and alumina, respectively.
The mullite-made jig and the alumina-made ring have been found to have the following drawbacks.
(1) A deflection yoke to be fired is made of ferrite containing MnO, ZnO and, as the main component, Fe.sub.2 O.sub.3. The MnO and ZnO components in ferrite react with Al.sub.2 O.sub.3 in mullite (Al.sub.2 O.sub.3 --SiO.sub.2) of jig to form a spinnel phase. Formation of the spinnel phase gives rise to volume expansion and consequently dimensional error.
Moreover, a mullite-made jig is porous, and further reacts with some components of deflection yoke and tends to form a vitreous layer; as a result, the deflection yoke after firing has dimensional changes (dimensional errors) in inner diameter, etc. and has no sufficient roundness.
(2) When an alumina-made ring is used, it reacts with some components of deflection yoke to be fired, to form a spinnel phase; as a result, the deflection yoke after firing has larger dimensions due to expansion, the inner and outer surfaces have strains, and the deflection yoke has no sufficient roughness. Furthermore, when the alumina-made ring is used by being fitted into the dent of a jig, the dimensional expansion of ring may bring about the destruction of jig.
Moreover, since the above reactions take place at the interface between jig and material to be fired or between ring and material to be fired, the material to be fired gives rise to component change at the interface, incurring deterioration in properties (e.g. strength) of material after firing.